1. Technical Field
The present disclosure generally relates to systems for providing quality control with respect to color printing production. More particularly, the present disclosure relates to devices, systems and methods for measuring the color bar of a printing sheet in conjunction with color printing press operation.
2. Background Art
Most color printing press machine manufacturers allow sheet-fed printing presses to be electronically controlled automatically via a so-called ‘closed loop’ system. Such a closed loop system can ensure that the inking units of the printing presses are adjusted properly so as to ensure that the desired ink density is applied, and that the plate cylinder register is adjusted properly for the correct alignment of printed color dot layers.
One well-known way of evaluating printed ink density, correlated to ink key position across the printing press, is to print a so-called ‘color bar’ across each sheet. A typical color bar can be a linear array of up to 100 or more color control patches. The color bar typically has a predetermined color composition and exhibits predefined geometric parameters relating to each ink control zone, as well as the position on the printing sheet.
Currently in the color printing press field, there are products that are able to rapidly measure the color bar to help automatically control the quality of color. Many of the most recent such measurement devices are configured to connect directly to closed loop system such that the associated color measurements are fed directly to software systems for making automatic adjustments to the printing press inking units. At the high end of products in this market, several intelligent systems are configured to control the position at which, or along which, color measurements are made, while simultaneously executing rapid automated scans of printed color bars. For example, the IntelliTrax system marketed by X-Rite, Inc. of Grand Rapids, Mich. includes a precision color measurement engine for color bar scanning, wherein the color measurement engine is subjected to fully automatic tracking and motion control (e.g., X and Y directional automation). Such automatic tracking of the color bar typically reduces or eliminates the need for operators to be vigilant with respect to minor misalignments as between the associated color measurement engine and the printing sheets being scanned thereby.
By contrast, with respect to the middle and lower end of quality control systems in the color printing press market, the quality of color measurement information collected from the printing sheet under scan will typically be greatly influenced by the degree to which the printing sheet is properly aligned with the associated color measurement engine. More particularly, to the extent the color information collected by a color measurement engine with respect to a target color bar incorporates or includes extraneous information collected from regions of the printing sheet that are disposed adjacent to, or that surround, the color bar, such extraneous information can render the overall color measurement associated with the particular scanning event invalid. For example, on such an occasion, the overall color measurement associated with the scanning event could report inaccurate color density values for the target color bar (e.g., color density values that are either too high or too low as compared to the true or objective color density value with which the target color bar may properly be associated).
With respect to printing press operation, the degree of confidence a user is able to place in the integrity of quality control color measurement information can be critical. In this regard, a so-called ‘worst case’ scenario may arise wherein a user employing a closed loop system to operate a high-speed printing press is not aware that color measurements are or have become contaminated (e.g., because of incorrect color or density feedback). In such circumstances, a large volume of printed goods that are either unusable or of degraded quality could potentially be produced in rapid succession before the user is even alerted to the problem. Such users therefore typically place a high premium on avoiding situations in which a color measurement value associated with a target color bar is inappropriately recognized or reported as valid.
Thus, despite efforts to date, effective devices, systems and methods for reducing and/or eliminating circumstances in which corrupted or contaminated color measurement information is inappropriately recognized as valid generally remain both necessary and desirable. More specifically, a particular and continuing need for such devices, systems and methods exists on the part of users employing middle to lower end quality control systems to assist in the operation of high-speed printing presses. These and other needs and desires are addressed and/or overcome by the devices, systems and methods disclosed herein.